C:\>type flock.pl

use Fcntl qw(:flock);

print "This is $^O\n";

open  FILE, ">>test.txt" or die "Oops $!\n";
flock FILE, LOCK_EX or die "Can't flock $!\n";
close FILE;

C:\>perl flock.pl
This is MSWin32
flock() unimplemented on this platform at flock.pl line 6.

C:\>